Transistor tone generating system using transistorized keying means



Oct. 16, 1962 H. o. SCHWARTZ TRANSISTOR TONE GENERATING SYSTEM USING TRANSISTORIZED KEYING MEANS Filed May 11, 1959 a S W m m\l\ WWQRM. NW WQW N NNx W YWQRQ w r Li H M E w Q QN mm m EN w g N UQ l N E s S-k Qkh 9BR IRE m m E mm a w XS .7 XE x5 SR EW wfi Q2 x Q \RWJ \-R\ Q! $5M kw United States atent Ohio Filed May 11, 1959, Ser. No. 812,302 1 Claim. (Cl. 841.01)

This invention relates to electronic musical instruments, and more particularly to a transistor tone generating system using transistorized keying means.

The frequency of the oscillators or tone generators of an electronic musical instrument must be quite stable in order to produce desirable musical tones. Oscillators which are extremely stable tend to be rather expensive, and it therefore is undesirable to provide an extremely stable oscillator for each note. One scheme for avoiding this is to provide one octave of extremely stable oscillators with the oscillators of this octave serving as master oscillators, and with an accompanying series or string of slave oscillators controlled by each master oscillator. Theoretically, it would be possible to place the master oscillators in the lowest octave, and to use successive frequency doublers for producing the remaining octaves of an electronic musical instrument. However, it is preferable that the master oscillators comprise the upper octave, with the slave oscillators comprising frequency dividers. This minimizes frequency deviation by dividing any deviation of the master oscillators, rather than multiplying them. Furthermore, components for the higher frequency oscillators tend to be somewhat smaller, and hence are more readily placed in an electronic musical instrument. In addition, such components tend to be less expensive.

In a master-slave, or divider type of electronic musical instrument, as just outlined, it is obvious that the oscillators must almost necessarily all be oscillating at all times. It will be apparent that a slave oscillator could not be placed in oscillationwithout also having the master oscillator in operation, and it also will be apparent that there is necessarily at least a slight time delay before the frequency of oscillation becomes entirely stable. There is a problem of rendering the oscillations of an oscillator effective when a key is depressed. Direct connection from the oscillator to the amplifier through a key switch, even when taken in connection with filter circuits, is undesirable due to reaction on the oscillators, and to the difficulty of controlling the attack and decay of the tone and avoiding key clicks.

It is an object of the present invention to provide an improved electronic musical instrument having a transistor oscillator and a transistor key switch in association therewith.

It is another object of this invention to provide an electronic musical instrument having a tone connecting switch arrangement wherein the switch is not in a direct tone path.

More particularly, it is an object of this invention to provide an electronic musical instrument having an oscillator tone output path connected through the collector and the emitter of the transistor, the key switch and associated components being connected to the base.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating the tone generators of the invention; and

FIG. 2 is a schematic wiring diagram illustrating one oscillator divider stage and a corresponding switching circuit.

3,fi58,3l Patented Oct. 16, 1962 Referring now to FIG. 1, there will be seen a master oscillator (M.O.) indicated at 10. This master oscillator may be of any desired type of high frequency stability, and generally may be expected to produce a sine wave as indicated immediately above the oscillator. The remaining or divider oscillators are of the Eccles-Jordan type, and these are not responsive to the sine wave. Accordingly, there is provided a butter amplifier (B.A.) indicated at 12, and provided with a transistor switch indicated at 14. The buffer amplifier may be of any desired overdriven type to produce substantially a square wave, as indicated above and to the right of the amplifier. The buifer amplifier drives a first divider amplifier 16, having an accompanying switch 18. The first divider, in turn, drives a second divider 20 having a switch 22, and this amplifier drives a third divider amplifier 24 having a switch 26. The third divider amplifier drives a fourth divider amplifier 28, having a switch 30. The fourth divider amplifier drives a fifth divider amplifier 32, having a switch 34, and this amplifier drives a sixth divider amplifier 36, having a switch 38.

A typical divider stage and the accompanying transistorized key switch are shown in FIG. 2, for example the first divider 16 and the accompanying transistorized switch 18.

The divider oscillator 16 is of the Eccles-Jordan type, as previously indicated, and includes a transistor 40 having a base 42, an emitter 44, and a collector 46'. The divider oscillator further includes a second transistor 48, of the same type, and including a :base 50, an emitter 52, and a collector 54.

The emitter 44 of the transistor 40 is grounded, while the collector is connected through a resistor 56 to a DC. supply line 58. The collector 46 is joined to the resistor 56 at a junction 60, and this junction is connected by a resistor 62 and a capacitor 64 in parallel therewith to a junction 66 connected to the base 50 of the second transistor 48, thereby comprising a half of the usual cross coupling in an Eccles-Jordan circuit. Similarly, the collector 54 is connected through a load resistor 68 to the 11C. supply line 58, and also is connected through a resistor 70 and capacitor 72 in parallel therewith to the base 42 of the first transistor 40. The emitter 52 of the second transistor also is grounded.

A connection is made through a resistor 74 from the base 42 to a junction 76, and a similar connection is made through a resistor 78 from the base 50 and junction 66 to the junction 76'. The junction 76 is connected by means of a suitable wire and other circuit means to the next preceding stage as indicated at 80. As will be appreciated, this preceding stage would be the butter amplifier 12 in a specific example, but would be any of the divider oscillators in connection with subsequent stages.

The output to the next divider stage is taken from the divider oscillator 16 preferably from the collector 46. Specifically, a voltage divider comprising a resistor 82 and a resistor 84 is connected to the collector 46, the bottom end of the voltage divider being grounded. An intermediate tap 86 on the voltage divider leads through a capacitor 88 to a wire or the like 90 leading to the next or succeeding divider stage.

The transistor switch 18 comprises a transistor 92 having an emitter 94, a base 96, and a collector 98. The collector 98 is connected through a load resistor 100 to the DC. supply line 58. The emitter 94 is grounded through a resistor 102. The emitter also is connected through a wire or the like 104 to the output, comprising one of the tones of the musical instrument, usually connected to an amplifier. The collector 98 also is connected through an isolating resistor 106 to the collector 54 of the second transistor 48 of the divider oscillator 16.

The base is connected to a filter 107 and through a resistor 109 to positive D.C., it being noted that the supply line 58 is minus DC. A reverse bias is applied to transistor base to insure complete cutofi. Since there is an appreciable resistance from base to ground, a small leakage current would bias the transistor into a conducting state. In addition at elevated temperatures the collector current would increase, hence starting conduction. The reverse bias will eliminate both problems. The filter 107 comprises a series resistor 108 connected at a junction 110 to the base 96, and connected at the other end to a junction 112. A second series resistor 114 is connected from the junction 112 to a junction 116, and this junction is connected to a junction 118, and hence to a key switch 120 leading to a source of DC. potential as indicated at V. The filter 107 further includes a capacitor 122 connected from the junction 110 to ground, a capacitor 124 connected from the junction 112 to ground, and a resistor 126 connected from the junction 116 to ground. There is also a sustain network including a capacitor 128 connected to the junction 118 and further including a resistor 130 connected to the capacitor 128, and a sustain switch 132 is connected from the resistor 130 to ground. The switch 132 normally is closed for a long sustain, and normally is open for a short sustain.

As will be understood, there are 13 master oscillators 10, one for each note or semi-tone of the highest octave of an electronic musical instrument. There is also one butler amplifier for each master oscillator, and a string of divider oscillators for each master oscillator. All of the master oscillators, buffer amplifiers, and divider oscillators operate at all times that the musical instrument is plugged in and turned on. When it is desired to play a note, the appropriate key switch, for example the key switch 120, is closed by depressing a key of the instrument. This allows the potential on the base 96 to increase at a rate determined by the filter 107, to provide a controlled attack of the note being played. As will be understood, the transistor 92 becomes conductive (whereas it is normally cut off) in accordance with the change of the potential on the base 96. Hence, the emitter-collector current increases at the rate effected by the filter 107, and the output at 104 increases at this same rate. When the key is released, the switch 120 is opened, and the potential on the base decreases or decays under the control of the filter 107, the output thus similarly decaying. There is a relatively fast attack and decay with the sustain switch 132 open. When the sustain switch 132 is closed, the capacitor 128 charges through the resistor 130 whenever the key switch 120 is closed. Thus, the attack of the note is considerably delayed. Similarly, when the key switch 120 is subsequently open, the capacitor 128 must discharge through the resistor 130, through the filter 107, and through the transistor 92. Thus, the decay is slowed, and the note is sustained.

The actual keying as effected by the key switch 120 4 is in the low impedance side of the transistor 92, and hence key clicks are literally swallowed up by the transistor 92, as well as by the filter 107. The input and output of the transistor switch are in the high impedance side, and interaction is substantially eliminated.

The specific example of the invention as herein shown and described is for illustrative purposes only. Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of this invention insofar as they come within the spirit and scope of the appended claim.

The invention is claimed as follows:

An electronic musical instrument comprising a plurality of master oscillators of high stability and a plurality of strings of divider oscillators of lesser stability comprising Eccles-Jordan oscillators respectively connected to and controlled by said master oscillators, said master oscillators and said divider oscillators oscillating continuously, all of said oscillators having high impedance outputs, and switch means for rendering said oscillators effective to produce audible tones from an electro acoustic transducer, comprising a plurality of transistors, one for each of said master and divider oscillators, and each having high impedance input means, high impedance output means, and a low impedance connection, respective means normally biasing each transistor to a nonconducting state, means respectively connecting the high impedance input means of each transistor to the corresponding oscillator high impedance output, a plurality of normally open playing key controlled switches, potential means connected to said key controlled switches, and means respectively connecting said playing key conrolled switches to said low impedance connections of said transistors for selectively biasing said transistors to conducting states upon selective closing of said playing key controlled switches.

References Cited in the file of this patent UNITED STATES PATENTS 2,295,524 Hanert Sept. 8, 1942 2,301,871 Hanert Nov. 10, 1942 2,401,372 Rienstra June 4, 1946 2,584,990 Dimond Feb. 12, 1952 2,639,639 Schmidt May 26, 1953 2,831,984 Ebers et al. Apr. 22, 1958 2,848,653 Hussey Aug. 19, 1958 2,885,570 Bright et a1. May 5, 1959 2,892,103 Scarbrough June 23, 1959 2,909,675 Edson Oct. 20, 1959 2,922,151 Reeling Jan. 19, 1960 2,935,626 MacSorley May 3, 1960 2,970,227 Horton Jan. 31, 1961 OTHER REFERENCES Douglas: Electronic Engineering, July 1958, pages 420-423. 

